Power supplies may be used in electronic applications to convert an input voltage to a desired output voltage in order to power one or more electronic devices. The power supplies that perform the voltage conversion may be linear power supplies or switched-mode (or switching) power supplies (SMPS). A linear power supply provides a desired output voltage by dissipating excess power in ohmic losses, such as by dissipating heat. A switching power supply may be substantially more efficient than a linear power supply because of the switching action.
Switching power supplies may include a boost inductor in connection with the switch. When the switch is on, the boost inductor is being charged. When the switch is off, the energy stored in the boost inductor is sent to the output of the switching power supply. Operation of the switch may be controlled by a controller module. The controller module is powered using a bias voltage that is drawn from the input voltage. Typically, the voltage required to power the controller module is much lower than the input voltage. In order to step-down the voltage, a resistor having a large resistance or a transistor operating in the linear region may be used. However, using these approaches results in large amount of power being wasted and dissipated as heat.
To have an efficient bias voltage generation, a boost inductor having a main winding and an auxiliary winding may be used. With both the main winding and the auxiliary winding, the boost inductor, functioning as a transformer, transfers charge from the main winding of the inductor to the auxiliary winding. The auxiliary winding uses the charge to supply bias to the controller module. A turns ratio of the main and auxiliary windings is a critical feature of the inductor. In order to have the correct turns ratio, the inductor is often custom manufactured since off-the-shelf inductors having the required turns ratio may not be available. However, the manufacture of custom inductors may be costly.